208 ELEMENTAKY STUDIES IN INSECT LIFE 



within the borders of the State. The insect fauna of 

 Iowa consists of all the insect life existing within the 

 borders of the State. State lines, however, have no 

 influence in themselves upon the distribution of species, 

 so that the fauna of Iowa and that of the adjoining 

 States of Missouri and Illinois would probably vary 

 but little. 



Zones of Life. The continent of North America may 

 be divided upon the lines of animal and plant distribu- 

 tion into three primary transcontinental regions: 

 Boreal, Austral, and Tropical. 



The Boreal region covers the whole of the northern 

 part of the continent, from the polar seas southward 

 to the northern boundary of the United States. A nar- 

 row strip along the Pacific coast and the higher por- 

 tions of the Sierra Cascades, the Rocky Mountains, and 

 the Alleghanies, all in the United States, are in this 

 life zone. 



The Austral region covers the whole of the United 

 States except the Boreal mountains and the Tropical 

 lowlands. 



The Tropical region covers the southern part of 

 the peninsula of Florida, the greater part of Central 

 America, the lowlands of southern Mexico south of the 

 table-land, and a narrow strip on each side of Mexico. 

 This strip follows the coast northward into the United 

 States. 



The fauna and flora --that is, the animal and plant 

 life within each of these regions are not alike 

 throughout the respective regions. They show striking 

 differences. This has led to the subdivision of these 

 principal zones into a number of minor areas based 



